The present invention relates generally to the recovery and/or production of solid, liquid and gases hydrocarbon products from coal and other carbonaceous materials, and more particularly to a novel method for producing and/or recovering relatively large amounts of methane and higher homologues thereof, oil, and a clean, high-carbon char from coal and other carbonaceous materials.
Prior to World War II, fuel gas was produced or manufactured in Europe and in the United States by the destructive distillation of coal. However, such manufactured gas had a relatively low heat rating, i.e. 475-560 B.t.u. per cubic foot, and accordingly, when natural gas became plentiful in the United States after World War II, it quickly replaced the manufactured gas because the former had a relatively high B.t.u. rating of about 1,030. Unfortunately, the consumption of gas has been steadily increasing in the United States, and the supplies thereof have been decreasing.
Because of problems with the dwindling supplies and availability of natural gas and gasoline, there has been renewed interest in the United States in the production of gas and oil from such carbonaceous materials as coil, oil shale and tar sand. Much of such attention has been directed to the use of coal as a source of such gas and oil because coal is relatively plentiful in the United States, and is found in 30 of the 50 states. It has been stated that at the present rate of consumption, the proved coal reserves in the United States would not be exhausted for some 600 years, and even if coal were to become the sole source of energy for the United States, the total reserves would be sufficient for close to 100 years even with the normal projected increases in the consumption of gas and oil.
The apparatus and processes which are presently being investigated for the commercial production of gas from coal are described in the March 1974 issue of Scientific American magazine and the November 1973 issue of Fortune magazine. The two systems which are apparently receiving the greatest amount of attention are the Lurgi process and the Koppers-Totzek process. However, neither of these processes appear to be the answer to the problem. Thus, both produce a gas which is basically a mixture of carbon monoxide and hydrogen, plus a small amount of methane, and with a heating value in the neighborhood of 300 B.t.u. per cubic foot . . . far below the B.t.u. rating of 1030 for natural gas. Also, such a gas could not be used generally because carbon monoxide is poisonous.
Other problems with the aforementioned processes are that they both require oxygen and steam in large quantities. Also, the Lurgi process requires coal of a particular size, and a coal which is substantially non-caking so that it will not form a solid mass and prevent the passage of gas through the coal bed during the extraction process.
Other processes are currently being investigated for the production of a high B.t.u. gas, but they are all expensive and relatively complicated.
Numerous patents have also issued, showing and describing various types of apparatus and processes for the production of gas and oil from coal and the like, but none appears to be commercially acceptable. Representative of these U.S. patents are Nos. 1,257,772; 1,378,643; 1,407,018; 1,458,357; 1,479,827; 1,482,342; 1,658,143; and 3,475,279. In these processes, coal, shale, or tar sand is moved either over heated walls, under heated walls, through heated stationary cylinders or through heated rotating cylinders, or into and through hot molten metal; by means of endless conveyors or screw conveyors; in the presence or the absence of air; either at a constant temperature or at a temperature which increases from the inlet to the outlet; and with the gas and vapors being removed from either the end, or the top or from the bottom of the retort.
With the exception of U.S. Pat. No. 3,475,279, few, if any, discloses the amounts or the analysis of the purported by-products. In the last mentioned patent, it is stated that the approximate yield per ton of coal processed has been 37 gallons of tar or heavy oil and 1950 cubic feet of gas having a heating value of approximately 919 gross B.t.u. per cubic foot. Although the heat content of the gas approaches the heating value of natural gas, the volume of gas produced is relatively low. Also, in said process it is apparently necessary to have an airtight system and to maintain pressure within the heating chamber near atmospheric pressure and the pressure in the coal bed slightly below atmospheric pressure . . . which might be difficult to accomplish.
With the aforementioned limitations and deficiencies of known apparatus and processes in mind, it is a general object of the present invention to provide a novel method for directly converting coal and other carbonaceous materials into usable hydrocarbon products. More particularly, it is an object to obtain relative large amounts of high Btu gases, low-sulfur oil, and a high-carbon char from coal and other carbonaceous materials, employing a single-stage, continuous process which does not require the addition of steam and/or oxygen, nor require extremely high temperatures or pressures.
More particularly, one of the primary objects of the present invention is to obtain directly from untreated coal which can contain rocks and other debris, a gas which has a Btu content substantially the same as "natural" gas. Specifically, it is an object to directly obtain such a gas from coal, which contains a relatively large amount of methane and the higher homologues thereof, without the necessity of going through a separate methanation step or process.
Another primary object of the present invention is to produce a clean-burning carbon char from coal and like carbonaceous materials.
Yet another primary object is to produce from coal and like carbonaceous materials, lumps or small masses of char which have a relatively large surface area or reactive carbon and which are relatively free of tars and other repolymerized hydrocarbon components. Specifically, it is an object of this invention to directly produce from coal, highly reactive carbon masses with large surface areas, which masses are substantially free of gases, tars, and repolymerized hydrocarbon components.
Another object of the present invention is to provide a novel method for obtaining hydrocarbon products directly from coal and other carbonaceous feed materials without pretreating the feed material.
A further object is to provide a novel method for obtaining hydrocarbon products directly from coal and other carbonaceous feed materials without the use of high pressure and/or high temperatures.
I have discovered that the above objects and advantages are achieved by continuously moving a mass of coal or other carbonaceous feed material through an elongated tube or pipe-like heat chamber maintained at a temperature of between about 1100.degree. F. and 1800.degree. F. throughout its length, in the absence of air and/or oxygen, with the feed material being turned or stirred as by means of a screw conveyor as it passes through the heat chamber, and with the gases and vapors being removed from the heat chamber adjacent the outlet end thereof by means of a vacuum of from about two inches to five inches of mercury. Based upon present information, it appears that the relatively high temperature in the tube adjacent the inlet, the stirring of the feed material to expose it to the heat, and the vacuum which exists throughout the length of the tube causes a sudden, deep "shock" heating of the feed material, such that the gases and vapors virtually "explode" therefrom. Thus, the heat causes a vigorous expulsion of the vapors and gases from the feed material and the vacuum causes said vapors and gases to be pulled through the churning bed of feed material in contact with the carbon, as compared with permitting the gases and vapors to slowly percolate through the bed and be withdrawn at regular intervals along the length of the tube. Also, it appears that the small amounts of transition metals in coal and tar sands such as iron, copper and nickel . . . or the metal of the tube . . . act as catalysts, whereby the steam produced from the water in the coal and tar sands is reduced to possibly a metal oxide and highly reactive hydrogen, and the hydrogen combines with the free carbon to form methane and the higher homologues of methane.